Respirators are commonly worn over the breathing passages of a person for at least one of two common purposes: (1) to prevent impurities or contaminants from entering the wearer's respiratory system; and (2) to protect other persons or things from being exposed to pathogens and other contaminants exhaled by the wearer. In the first situation, the respirator is worn in an environment where the air contains particles that are harmful to the wearer, for example, in an auto body shop. In the second situation, the respirator is worn in an environment where there is risk of contamination to other persons or things, for example, in an operating room or clean room.
Some respirators are categorized as being “filtering face-pieces” because the mask body itself functions as the filtering mechanism. Unlike respirators that use rubber or elastomeric mask bodies in conjunction with attachable filter cartridges or filter liners (see, e.g., U.S. Pat. RE39,493 to Yuschak et al. and U.S. Pat. No. 5,094,236 to Tayebi) or insert-molded filter elements (see, e.g., U.S. Pat. No. 4,790,306 to Braun), filtering face-piece respirators have the filter media extend integrally throughout the whole mask body so that there is no need for installing or replacing a filter cartridge. As such, filtering face-piece respirators are relatively light in weight and easy to use.
Filtering face-piece respirators generally fall into one of two categories, namely, flat-fold respirators and shaped respirators. Flat-fold respirators are stored flat but include seams, pleats, and/or folds that allow the mask to be opened into a cup-shaped configuration for use. Examples of flat-fold filtering face-piece respirators are shown in U.S. Pat. Nos. 6,568,392 and 6,484,722 to Bostock et al. and 6,394,090 to Chen.
Shaped respirators, in contrast, are more-or-less permanently formed into a desired face-fitting configuration and generally retain that configuration during storage and use. Shaped filtering face-piece respirators regularly include a molded supporting shell structure, generally referred to as a “shaping layer”, which is commonly made from thermally bonding fibers or an open-work plastic mesh. The shaping layer is primarily designed to provide support for a filtering structure. Relative to the filtering structure, the shaping layer may reside on an inner portion of the mask (adjacent to the face of the wearer), or it may reside on an outer portion of the mask, or on both inner and outer portions. Examples of patents that disclose shaping layers for supporting filtration layers include U.S. Pat. No. 4,536,440 to Berg, U.S. Pat. No. 4,807,619 to Dyrud et al., and U.S. Pat. No. 4,850,347 to Skov.
In constructing a mask body for a shaped filtering face-piece respirator, the filtration layer is typically juxtaposed against the shaping layer, and the assembled layers are subjected to a molding operation by placing the assembled layers between heated male and female mold parts (see, for example, U.S. Pat. No. 4,536,440 to Berg) or by passing the layers in superimposed relation through a heating stage and thereafter cold molding the superimposed layers into the face mask shape (see U.S. Pat. No. 5,307,796 to Kronzer et al. and U.S. Pat. No. 4,850,347 to Skov). The filtration layer generally assumes the curved configuration of the molded shaping layer.
When a shaping layer is made from a plastic mesh like the filtering face-piece respirator described in the '347 patent to Skov, the shaping layer or mesh generally resides in a spaced or unjoined relationship to the filtering structure except at the mask perimeter and where a valve is mounted to the mask body. FIG. 1 shows a known respirator 100 that has a mesh 102 as a supporting structure. FIG. 2 shows that there is a gap 104 that commonly resides between the mesh 102 and the filtering structure 106. The unjoined relationship 104 between the mesh 102 and the filtering structure 106 does not allow for the filtering structure 106 to be fully supported by the mesh 102 such that the filtering structure 106 remains juxtaposed against the mesh 102 over the whole surface of the mask body. As such, opportunities exist for the filtering structure to be pulled inwardly, particularly when the wearer inhales and the mask has been exposed to high levels of humidity or moisture for an extended time period. The failure of the filtering structure to closely follow the outer mesh also leaves an appearance that is generally unsightly. The invention described below seeks to overcome these issues or problems in the molded filtering face-piece respirator art.